Vasoactive intestinal peptide and anterior pituitary function

Cellular and molecular specificity of pituitary gland physiology

The anterior pituitary gland has the ability to respond to complex signals derived from central and peripheral systems. Perception of these signals and their integration are mediated by cell interactions and cross-talk of multiple signaling transduction pathways and transcriptional regulatory networks that cooperate for hormone secretion, cell plasticity, and ultimately specific pituitary responses that are essential for an appropriate physiological response. We discuss the physiopathological and molecular mechanisms related to this integrative regulatory system of the anterior pituitary gland and how it contributes to modulate the gland functions and impacts on body homeostasis.

Oxytocin enhances the prolactin response to vasoactive intestinal polypeptide in healthy women

OBJECTIVE

To establish whether oxytocin modifies the stimulatory effect of vasoactive intestinal polypeptide (VIP) on prolactin secretion in healthy women.

DESIGN

Controlled clinical study.

SETTING

Healthy women in an academic research environment.

PATIENT(S)

Seven healthy women (aged 24-32 years) were tested on the 22nd day of two consecutive normal menstrual cycles.

INTERVENTION(S)

Vasoactive intestinal polypeptide (4 pmol x kg(-1) x min(-1) in 50 mL of normal saline infused i.v. for 60 minutes) was administered in either the presence or absence of concurrent treatment with oxytocin (2 IU injected plus 0.07 IU/min infused for 60 minutes).

MAIN OUTCOME MEASURE(S)

Serum prolactin levels.

RESULT(S)

The administration of VIP induced a significant increase in serum prolactin levels, with a mean peak response 1.6 times higher than baseline at 45 minutes after injection. In the presence of oxytocin, the prolactin response to VIP was significantly higher, with a mean peak response 2 times higher than baseline.

CONCLUSION(S)

These data suggest that in healthy women, oxytocin facilitates the regulation of the stimulating effect of VIP on prolactin secretion.

Pituitary adenylate cyclase activating peptide (PACAP) mRNA in the rat neocortex

In agreement with previous studies, Northern blots revealed expression of pituitary adenylate cyclase-activating peptide (PACAP) mRNA in the rat cerebral cortex. In order to identify the cells expressing PACAP mRNA, semiquantitative in situ hybridization histochemistry was applied. A moderate concentration of PACAP mRNA transcripts was determined in the cingulate and frontal cortices, whereas lower concentrations were found in other cortical areas. In emulsion dipped sections, grains were detected over cell bodies in cortical layers II, III and IV. Grains were diffusely distributed over cells in the outer granular layer of the anterior cingulate and the retrosplenial areas. In the outer pyramidal cell layer a few neurons contained a large number of grains. These data show that PACAP mRNA is present in cells outside the hypothalamus and implies that PACAP could play a broader transmitter role in the CNS than earlier anticipated.

Changes of cerebral vasoactive intestinal polypeptide- and somatostatin-like immunoreactivity induced by noise and whole-body vibration in the rat

To clarify the role of vasoactive intestinal polypeptide (VIP) and somatostatin, somatotropin-release inhibiting factor, (SRIF) neurons in the response to organisms to noise or whole-body vibration stress, VIP- and SRIF-like immunoreactivity were determined in various regions of the rat brain following exposure for 90 min to noise (broad band, 102 dB) or whole-body vibration (20 Hz, 4.0 g). Both noise and whole-body vibration significantly increased VIP-like immunoreactivity in the amygdala. A significant reduction of VIP-like immunoreactivity in the hippocampus was induced only by whole-body vibration. On the other hand, SRIF-like immunoreactivity was decreased significantly in the hypothalamus and increased significantly in the amygdala by noise and whole-body vibration, respectively. The present findings would seem to indicate that the amygdalofugal VIP neural system is involved in regulating hypothalamic and pituitary hormone secretions in non-specific reactions to stress. Responses of hippocampal VIP and the amygdalofugal SRIF to whole-body vibration stress are assumed to be activated as specific reactions to the stress.

Determination of vasoactive intestinal peptide in rat brain by high-performance capillary electrophoresis

A high-performance capillary electrophoresis (HPCE) method for determining vasoactive intestinal peptide (VIP) in rat brain was developed. Cerebral cortex was first extracted by solid-phase extraction and purified by reversed-phase high-performance liquid chromatography. The VIP-rich fraction was further analysed by capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography using a commercial HPCE instrument with UV detection. The identity of the peak of endogenous VIP was confirmed by performing multiple CZE analyses at different pH values. This HPCE method allows VIP to be detected and measured with good molecular specificity and could represent a reference method to validate data obtained by radioimmunoassay.

Effect of paradoxical sleep deprivation on vasoactive intestinal peptide-like immunoreactivity in discrete brain areas and anterior pituitary of the rat

To determine whether vasoactive intestinal peptide (VIP) is involved in paradoxical sleep (PS) homeostasis, VIP-like immunoreactivity (VIP-LI) of discrete brain areas was determined by radioimmunoassay after 24 and 48 h of PS deprivation by the watertank technique followed or not by 5 h of sleep rebound. This study was carried out with an environmental control (placed in dry watertank: DWC) and a nonstressed control. Such PS deprivation induced a decrease of VIP content in PS-deprived rats restricted to cortex and anterior pituitary. In the cortex, the decrease in VIP-LI was of the same magnitude after 24 and 48 h of PS deprivation and VIP-LI was normal by 5 h of sleep rebound; as such a decrease was also observed after 48 h in DWC, it could be due to the stress related to the experiment rather than lack of sleep. In the anterior pituitary, the decrease was related to the duration of deprivation with a greater decrease in VIP-LI after 48 than after 24 h of PS deprivation and specifically related to PS deprivation since it was not observed in DWC rats. After 5 h of sleep rebound, recovery of VIP-LI was total in the 24-h experiment and partial in the 48-h one. In all eight other structures studied, VIP was unchanged after experimentation. These results strongly suggest that VIP is not involved in PS homeostasis but as indicated by other experiments more probably in circadian organization of sleep.

Daily variations in concentration of vasoactive intestinal polypeptide immunoreactivity in discrete brain areas of the rat

The concentration of VIP-like immunoreactivity (VIP-LI) was determined by radioimmunoassay at various times of the day in 11 discrete brain areas and in the antehypophysis of rats maintained on a regular 12 h/12 h light-dark cycle. In the suprachiasmatic and periventricular nuclei the VIP-LI increased during the dark period and decreased during the subsequent light period. In addition, the VIP-LI exhibited complex variations in the locus coeruleus, the periaqueductal gray matter and the paraventricular nucleus, but did not change in the other areas investigated.